Lord Adonis has been reshuffled away from education
The reshuffling of Andrew Adonis out of his post as schools minister in England is a threat to the academy programme, opposition parties have claimed.
Shadow schools secretary, Michael Gove, said academies would suffer from the government's "factional in-fighting".
Liberal Democrat children's spokesman, David Laws, predicted that the academy plans would be "strangled".
The Department for Children, Schools and Families has said it remains committed to having 400 more academies.
Lord Adonis, who has been reshuffled to the Department for Transport, has been strongly identified as a champion of academies - a flagship scheme developed when Lord Adonis was an adviser to former prime minister Tony Blair.
Academies were developed as a way of intervening in areas of England with high levels of disadvantage and low educational achievement, creating high-cost, high-profile schools with greater independence than other state schools.
They also have an external sponsor, such as businesses, faith groups or universities.
When Gordon Brown replaced Tony Blair as prime minister there was speculation about the future of the academy scheme, which had been so closely linked to the outgoing leader.
But Mr Brown committed his government to an acceleration of academies, using this model of secondary school as a way of regenerating educational performance in deprived areas.
The standards-raising National Challenge scheme launched by Schools Secretary Ed Balls, targeting schools where fewer than 30% of pupils get five good GCSEs including English and maths, could see the creation of dozens of academies.
But the reshuffling of government posts, which has seen Lord Adonis moved from being schools minister, has been viewed by opposition parties as a shift away from Tony Blair's education reforms.
Mr Gove said: "Everyone who believes in the integrity of the academies programme and the reform agenda in education will be disturbed to hear that Ed Balls has kicked Andrew Adonis out of the education department."
Liberal Democrat schools spokesman David Laws said the removal of Lord Adonis was a "disgrace" - and warned that academies would suffer as result of internal power struggles within the government.
"The real losers here will be thousands of children in some of the poorest parts of the country who were being targeted by the academies programme," said Mr Laws.
"We can now be sure that all of the momentum will seep away from the academies programme, which will continue to exist in form but not in substance."
In response, a DCSF spokeswoman set out the government's commitment to academies, which she says have had above-average improvements in GCSE results.
A DCSF statement says academies have become "popular with parents and heavily oversubscribed".
"In the relatively short time they have been operating, academies have made remarkable progress and the programme has been accelerated over the past year.
"The government is committed to opening 400 new academies - on current trajectory we will have achieved this by 2012."
Lord Adonis said that together with Schools Secretary Ed Balls he had "accelerated and strengthened" the academy programme.
"I am confident the country will want to stick with Labour investment and reform," he said.
Lord Adonis, a former journalist and prime ministerial adviser, was made a peer in 2005, allowing him to enter the government as a minister.
His involvement in academies has seen them evolve from a controversial experiment to being accepted as part of the educational landscape by the three main Westminster parties.
Last week the Conservatives opened the door to Lord Adonis's playing a role in a future Conservative government - with Mr Gove saying, "We are on the same page as Andrew Adonis".
As well as being associated with academies, Lord Adonis has been identified with a results-raising initiative in London secondary schools and with provision for gifted and talented pupils.
As an adviser and minister during the Blair administrations, he was an influential voice in education reforms, which have seen the introduction of greater diversity within the state system - such as specialist and trust schools.